The BATT Program is supported by the U.S. Department of Energy Office of Vehicle Technologies (OVT) and is part of the Lawrence Berkeley National Laboratory’s Carbon Cycle 2.0 initiative. BATT investigators in top research universities and institutions work on ten Task Areas: Anodes, Cathodes, Liquid Electrolytes, Solid Electrolytes, Cell Analysis, Diagnostics, Modeling, lithium-air batteries and sodium-ion batteries.
Xiao-Qing Yang and Kyung-Wan Nam, BNL
The high energy density Li-rich layered materials xLiMO2·(1-x)Li2MnO3 are promising candidate cathode materials for electric energy storage in plug-in hybrid electric vehicles (PHEVs) or electric vehicles (EVs). The relatively low rate capability is one of the major problems need to be resolved for these materials. In order to gain fundamental understanding to the key factors limiting the rate capability, in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) studies of the Li1.2Ni0.15Co0.1Mn0.55O2 cathode material has been carried out. Through these studies direct experimental evidence is obtained showing that Mn sites have a much poorer reaction kinetics both before and after initial “activation” of Li2MnO3, comparing with Ni and Co. These results indicate that the Li2MnO3 might be the key component limiting the rate capability of the Li-rich layered materials, providing valuable guidance in designing various Li-rich layered materials with desired balance of energy densities and rate capabilities for different applications.
Kristin Persson, LBNL
Li2MnO3 is a critical component in the family of the so-called ‘Li-excess’ materials, which are attracting attention as advanced cathode materials for Li-ion batteries. In this work, first-principles calculations are performed to investigate the electrochemical activity and structural stability of stoichiometric LixMnO3 (0 ≤ x ≤ 2) as a function of Li content. It is shown that the Li2MnO3 structure is electrochemically activated above 4.5 V on delithiation and that charge neutrality in the bulk of the material is mainly maintained by the oxidization of a portion of the oxygen ions: from O2− to O1−. While oxygen vacancy formation is found to be thermodynamically favorable for x < 1, the activation barriers for O2− and O1− migration remain high throughout the Li composition range, impeding oxygen release from the bulk of the compound. Furthermore, defect layered structures, where some Mn resides in the Li layer, become thermodynamically favorable at lower Li content (x < 1), indicating a strong tendency towards the spinel-like structure transformation. Concurrently, the calculated energy barriers for Mn migration from the Mn-layer into the Li-layer suggests a Li2MnO3 structural instability for x < 0.5. Based on the observations, a critical phase transformation path is suggested for forming nuclei of spinel-like domains within the matrix of the original layered structure. Furthermore, the formation of defect layered structures during the first charge manifests in a significant depression of the voltage profile on the first discharge, providing one possible explanation for the observed ‘voltage fade’ of the Li-excess materials.
Patrick Looney and Feng Wang Group at BNL
Ion exchange is an important method for preparing new cathode materials with metastable structures that are generally inaccessible via direct chemical reactions, but can be obtained via Li+ exchange of Na+ in iso-structural Na-containing compounds. Looney and Wang Group at Brookhaven National Laboratory have developed a new in-situ reactor for real time probing of ion exchange reactions, enabling quantitative measure of intermediate phases and reaction kinetics. In studies of Li+ exchange of Na+ in NaVPO5F compound, it was found that the reaction proceeds via a complicated phase transformation process, towards Li(Na)VPO5F — a new high-energy cathode. This new in-situ technique may also be applied for studies of other type of synthesis reactions, such as hydrothermal, solvothermal and solid-state. Real-time, quantitative identification of structure and phases during synthesis using time-resolved synchrotron XRD provides a new avenue for rational design and preparation of battery materials of desired phases and properties.
Yi Cui, Stanford University
A method was developed to synthesize Si porous structures for Si batteries directly from agricultural waste products rice husks. Rice husks were first converted to pure silica by burning in air and then reduced to silicon by magnesium. The synthesis process results in a 5 wt% yield of Si according to the weight of the initial rice husks. Considering the abundance (1.2×108 tons/year) and the low price (~$18/ton) of the rice husks, the synthesis dramatically reduces the cost of nanostructured silicon, which may paves the way for large scale application of Si anodes in vehicles.
Donghai Wang’s group at the Pennsylvania State University has developed novel, silicon-carbon (Si-C) composite that possesses primary carbon-coated sub-10 nm Si particles and secondary micro-sized aggregation. Because of this unique structure, the as-synthesized Si-C composite anode can deliver a high reversible specific capacity (~1600 mAh/g) with excellent cycling stability over 150 cycles.
Nitash Balsara, LBNL
Lithium-sulfur cells are attractive targets for energy storage applications as their theoretical specific energy of 2600 Wh/kg is much greater than the theoretical specific energy of current lithium-ion batteries. Unfortunately, the cycle-life of lithium-sulfur cells is limited due to migration of species generated at the sulfur cathode. These species, collectively known as polysulfides, can transform spontaneously, depending on the environment, and it has thus proven difficult to determine the nature of redox reactions that occur at the sulfur electrode.
Karim Zaghib, Hydro Quebec (Montreal, Canada)
The objective of this project is to develop high-capacity, low-cost electrodes with good cycle stability to replace graphite in Li-ion batteries. The challenge of this work is to stabilize the Si-anode capacity which requires studying the architecture of the electrode and controlling the stress.
Dean Wheeler and Brian Mazzeo of Brigham Young University (Provo, UT) have developed a new surface probe that can accurately measure electronic conductivity of intact electrodes. Measuring conductivity of intact thin-film electrodes (still attached to current collector) is difficult, and prior methods have not been sufficiently accurate and robust. The new method uses four small parallel lines to contact the surface with controlled applied pressure. The method also allows simultaneous measurement of bulk film conductivity and contact resistance between the film and the current collector.
Gao Liu at LBNL has developed a new kind of composite anode based on silicon that can absorb eight times the lithium of current Li-ion batteries and maintains a high capacity of 2100 mAh/g in Si after 650 cycles.
Yi Cui, Stanford University
Silicon is a promising next-generation anode material for high-energy lithium-ion batteries due to its high specific capacity, which is theoretically 10 times greater than graphite. However, its cycle life is limited due to volume expansion and fracture during lithium reaction. This degradation of the Si results in loss of electrical connection and pulverization of the electrode. Several fundamental studies still need to be conducted to develop viable Si electrodes for batteries. Yi Cui’s group at Stanford University is working on understanding the properties of various Si nanostructures and is designing new ones based on particles and wires that target improving Si cyclability.
The Zaghib Group at Hydro-Québec has used in situ SEM to see SiOx particles grow and shrink during cycling. SiOx is a promising anode material for Li-ion batteries due to a high theoretical specific capacity of 1338 mAh/g and less volume change than Si upon charge-discharge. Analysis of the morphology changes in SiOx particles provides insight into the failure mode associated with capacity fade on cycling.
The Persson and Kostecki Groups, in collaboration with other BATT investigators, have quantified lithium-ion diffusivity as a function of transport direction in graphite anodes. Electrochemical experiments combined with first-principles calculations indicate that lithium diffusion in graphite is several orders of magnitude faster in the direction parallel, as opposed to perpendicular, to the graphene plane. These results provide guidelines for designing graphite anodes with preferential orientation for higher rate capability, which translates to faster charging batteries.
BATT Scientist Prof. Nitash Balsara (UC Berkeley and Lawrence Berkeley National Laboratory) was selected as a new 2014 fellow of the Neutron Scattering Society of America (NSSA) for sustained, high impact, neutron scattering research on a broad range of polymeric materials, and for organizational, mentoring and leadership activities in promoting the use of neutron scattering […]
Gerbrand Ceder, MIT and Kristin Persson, LBNL made the cover of the latest Scientific American with their article: “How Supercomputers Will Yield a Golden Age of Materials Science”. Check it out!
Here’s the clip of Dr. Persson’s presentation, A Google for Materials